Logging and monitoring boreholes has been done for many years to enhance and observe recovery of oil and gas deposits. Data relating to earth formations are acquired by logging operations for purposes of exploration, development and management of hydrocarbon or water reservoirs, and sequestration of substances such as CO2. Such operations, including wireline logging, measurement-while-drilling (MWD) and logging-while-drilling (LWD), typically use a downhole tool having various sensing components for collecting, storing, and transmitting data.
In the logging of boreholes, one method of making measurements underground includes attaching one or more tools to a wireline connected to a surface system. The tools are then lowered into a borehole by the wireline and drawn back to the surface (“logged”) through the borehole while taking measurements. The wireline is usually an electrical conducting cable with limited data transmission capability.
Similarly, permanent monitoring systems are established with permanent sensors that are also generally attached to an electrical cable. After drilling a well, various sensing components may be fixed to production tubing for purposes of analyzing hydrocarbons and other fluids present in the wellbore, and for control of fluid flows in the wellbore. In this, various sensing components typically are used for purposes of production logging.
Long term reservoir monitoring and permanent monitoring are other applications that require deployment of sensors in completed wells. Sensor arrays may be deployed in a well by various means and sensor data gathered and transmitted uphole by a telemetry system for processing and analysis.
Recent developments in drilling technology require that downhole tools be capable of effectively collecting various data with high sensitivity or selectivity while drilling in oilfield or downhole environments. In this, there is a need for improved sensing systems that are able to acquire various data with high sensitivity or selectivity in a real-time manner.